There's lots of things you can use depending on what your dog likes. I don't use a lot of training treats but when I do it's a mixture of 'commercial' treats such as Nature's Menu chicken treats, Gravy Bones, Fish4Dogs Stars or JWB CrackerJacks; home-made stuff like tuna bread or livercake and 'fresh' stuff like small pieces of chicken, cheese, ham, apple, hotdog sausage etc. You can also use pieces of your dog's kibble as treats. There are lots more possibilities than what I've listed above, it really depends what your dog likes.
Generally it's best to find out what your dog really likes and save this real high value stuff for the important things like recall etc. Whatever you feed them make sure you take it into account in their overall diet and adjust their actual meals accordingly so that you're not overfeeding them.